The field of the invention is seatbelts of the type used in automobiles and aircraft, and the invention relates more particularly to reels of the type which permit the person who is strapped in the seat to move with relative freedom until the reel is locked. Upon sudden stopping, or other motion which causes a rapid withdrawal of the strap, the reel locks.
One reel assembly of the type used by pilots is manufactured by Pacific Scientific and operates by the relative movement of a flywheel with respect to a thrust plate. Three ball bearings are held in indentations in the flywheel and when the reel is moved rapidly, the flywheel lags behind the reel thus forcing the ball bearings out of the indentations and tripping a dog which stops the movement of a reel by engaging a ratchet wheel. The device is reset by reseating the balls, thus again holding the dog away from the ratchet wheel. This device has a very large number of parts and a number of these parts are used to prevent tripping by vibration and by the rapid retraction of the belt.
An inertia wheel was also used in the automobile seatbelt retraction wheel shown in U.S. Pat. No. 3,323,749. In this device, a nut moves upwardly and engages teeth on a cap when the belt is rapidly withdrawn from the reel. The device resets itself by gravity as a result of the weight of the nut. Such device would not be useful in aircraft since it relies on gravity and the position of an aircraft is not always horizontal.
Many reel assemblies of the type used in military aircraft must be manually reset once tripped. For some applications, it is beneficial to perform the resetting step automatically without the need for manual resetting.